The present invention relates to a flash lamp type device for illuminating an original document and, more particularly, to an original document illuminating device which for safety operation activates an alarm, a display and others by detecting the breakage of a glass platen and/or the open position of a protective cover and disenabling a trigger circuit which is associated with a trigger wire.
In electrophotographic equipment, a flash lamp type illuminating device usually includes a trigger wire which is provided around a flash lamp and applied with a predetermined high voltage to energize the flash lamp. To guarantee safety operation, that portion of the illuminating device in which the flash lamp is disposed is surrounded by a protective cover. In addition, when the protective cover is opened for the replacement of the flash lamp or maintenance, the power supply is automatically shut off by sensing the opening of the cover and/or by sensing the breakage of a glass platen so as to eliminate the fear of electric shock.
However, an illuminating device of the kind described further includes a main capacitor which is adapted to cause the flash lamp to glow and, for this purpose, charged with a high voltage. Even if the power supply to the interior of the device is stopped, there is a fear that a person touches the high-voltage section inside of the device to receive an electric shock when he or she opens the protective cover to replace the flash lamp or when the glass platen is broken.
In the light of the above, an arrangement may be made such that the open position of the protective cover occurring in the event of replacement of the lamp is sensed to automatically discharge the main capacitor and, thereby, cause the flash lamp to radiate. This kind of implementation against electric shocks is not fully acceptable, however, because a charged capacitor exists in a trigger circuit which is associated with the trigger wire. Specifically, a high voltage (13 to 10 kilovolts) is apt to be developed in the trigger wire due to malfunctions of the trigger circuit and/or those of a control section which are ascribable to, for example, noise introduced in a central processing unit (CPU) of a microcomputer. Consequently, when a person opens the cover to replace the lamp or when the glass platen is broken, he or she is not free from the fear of touching the trigger wire which would give an electric shock.